Process for preparing 4-aminodiphenylamine

ABSTRACT

A process for preparing 4-aminodiphenylamine having the steps of reacting nitrobenzene and aniline in the presence of a complex base catalyst, hydrogenating the reaction mixture with hydrogen, a powdery composite catalyst, and a hydrogenation solvent; separating, recovering, and reusing the complex base catalyst and the powdery composite catalyst from the reaction mixture; separating, recovering, and reusing aniline, and optionally water, from the reaction mixture; refining the reaction mixture to obtain 4-aminodiphenylamine. The complex base catalyst comprises tetraalkyl ammonium hydroxide, and tetraalkyl ammonium salt.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.11/477,954 filed on Jun. 30, 2006, now allowed, which in turn is acontinuation of U.S. Pat. No. 7,084,302 issued on Aug. 1, 2006, whichclaims priority on CN03148566.9, CN03148195.7, CN03148194.9,CN03148199.X, CN03148565.0, CN03148200.7, CN03148198.1, andCN03148196.5, all filed on Jul. 4, 2003 in China. The contents of allabove-mentioned priority applications and patents are incorporatedherein by reference in the entirety and for all purposes.

TECHNICAL FIELD

The present invention relates to a process for preparing4-aminodiphenylamine using nitrobenzene and aniline as raw materials.

BACKGROUND OF THE INVENTION

4-Aminodiphenylamine is an important intermediate of antioxidant andstabilizer, and is an important chemical product for rubber industry andpolymer industry. Depending on the starting materials, known methods forpreparing 4-aminodiphenylamine include:

(1) aniline method, where p-nitro-chlorobenzene and aniline as rawmaterials react in the presence of a catalyst to produce4-nitrodiphenylamine, then, 4-nitrodiphenylamine is reduced by sodiumsulfide to form 4-aminodiphenylamine;

(2) formanilide method, where formic acid and aniline are used asstarting materials to prepare formanilide, which in turn reacts withp-nitro-chlorobenzene in the presence of an acid-binding agent such aspotassium carbonate, to produce 4-nitrodiphenylamine, and then,4-nitrodiphenylamine is reduced by sodium sulfide to form4-aminodiphenylamine;

(3) diphenylamine method, where diphenylamine as raw material isnitrosated using a nitrite in an organic solvent to produceN-nitrosodiphenylamine, which is rearranged to 4-nitrosodiphenylaminehydrochloride under the action of anhydrous hydrogen chloride, and then,4-nitrosodiphenylamine hydrochloride is neutralized with a base to give4-nitrosodiphenylamine which is finally reduced to 4-aminodiphenylamineby sodium sulfide.

Although these methods use different starting materials, sodium sulfideis usually used as the reducing agent to prepare 4-aminodiphenylamine.These reactions suffer from severe reaction conditions, complexoperation, high energy consumption, low yield, high cost, andenvironment pollution caused by concomitant waste water, waste gas, andwaste residues.

Among the preparation methods for 4-aminodiphenylamine, some methods usenitrobenzene, nitrobenzene and aniline, or nitrosobenzene as rawmaterials to carry out condensation reaction, and then use hydrogen gasto perform hydrogenation to produce 4-aminodiphenylamine. In fact, itwas reported in 1901 (Wohl, Chemische Berichte 34, p. 2442 (1901)) and1903 (Wohl, Chemische Berichte 36, p. 4135 (1903)) that nitrobenzenereacted with aniline under the action of a base to form4-nitrosodiphenylamine and 4-nitrodiphenylamine. However, the method hadbeen neither regarded as important nor developed because of the relativelow yield until 1990s when it was researched and developed again andachieved some progress. See DE 19734055.5, DE 19810929.6, and DE19709124.5. However, the methods as disclosed in the art havedisadvantages.

First, the catalysts used in these methods are expensive, which resultsin relatively high production cost in an industrial-scale production.Thus, these methods have no advantage over other conventional methods.For examples, tetraalkyl ammonium hydroxide and fluoride used incondensation reaction and noble metal, such as palladium, platinum,rhodium, and the like, used in hydrogenation reaction are expensive. Theinstability of tetraalkyl ammonium hydroxide imparts some difficulty tothe recovery and reuse of tetraalkyl ammonium hydroxide. In addition,the use of noble metal hydrogenation catalysts applies higherrequirements to raw materials and equipment. Second, the yield isrelatively low, which makes the methods only suitable for laboratoryresearch. This is why these methods have been difficult to beindustrially applied. Third, the operation is complicated. These methodsare not in favor of continuous operations, which limits the productionscale. Fourth, separation is difficult and purity of product is nothigh.

U.S. Pat. No. 6,395,933 discloses a process for synthesizing4-aminodiphenylamine by reacting nitrobenzene and a substituted anilineat a certain temperature in the presence of a strong base and aphase-transfer catalyst. The process is not satisfactory in yields, andthere are many side reactions. In the product mixture of4-nitrodiphenylamine and 4-nitrosodiphenylamine, the proportion of4-nitrodiphenylamine is too high which indicates that too much hydrogenhas been consumed during the hydrogenation reaction and the productioncost is thereby significantly increased. Furthermore, the process needsan oxidizing agent, which makes it unsuitable for industrial production.

WO 93/00324 discloses a process for preparing 4-aminodiphenylamine byreacting nitrobenzene and aniline at a proper temperature in a propersolvent in the presence of a base with the contents of proton materialsin solution being controlled. The process requires a solvent and thecontrol of the contents of proton materials in the solution. Theintroduction of the solvent results in increased energy consumption anddifficulty for separation. Controlling the contents of proton materialsgives rise to difficulty for operation and control of the reaction. Inparticular, at a later stage of the condensation reaction, controllingthe contents of proton materials, which mainly means dehydration tolower water content, prolongs the reaction time and causes partialaniline to be entrained out. The later stage, the more difficultremoving the proton materials. Controlling the proton materials at acertain range is difficult, and goes against industrial production. Theexpensive tetraalkyl quaternary amine base catalyst will quicklydecompose in the course of controlling the contents of proton materialsto a range of from 0.5 to 4 percent, resulting in increased productioncost.

SUMMARY OF THE INVENTION

The present invention provides a continuous process for preparing4-aminodiphenylamine, which uses nitrobenzene and aniline as thestarting materials, a complex base catalyst as a condensation catalyst,and a powdery composite catalyst as a hydrogenation catalyst. Theprocess of the present invention comprises five stages:

1. condensation;

2. hydrogenation in the presence of a hydrogenation solvent;

3. separating, recovering, and reusing the complex base catalyst, andseparating, recovering, and reusing the powdery composite catalyst whichis optionally at least partially regenerated;

4. separating, recovering, and reusing aniline, and optionally,separating, recovering and reusing the hydrogenation solvent;

5. refining.

The present invention uses inexpensive catalysts with good yields incondensation and hydrogenation reaction and provides a process suitablefor industrial scale production and continuous production of4-aminodiphenylamine.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow chart showing an embodiment of the present inventionfor preparing 4-aminodiphenylamine. The reference numbers are: 1—powderycomposite catalyst; 2—hydrogenation solvent; 3—reused complex basecatalyst; 4—reused, optionally at least partially regenerated, powderycomposite catalyst; 5—reused hydrogenation solvent; 6—reused aniline;7—condensation liquid; 8—hydrogenation liquid; 9—aqueous phase obtainedby evaporation in concentration process and organic phase obtained byextraction; 10—crude product of 4-aminodiphylamine.

FIG. 2 is a schematic diagram illustrating a gas-aid falling filmevaporator used in an embodiment of the process of the presentinvention. The reference numbers are: 1′—condensed water outlet;2′—shell pass; 3′—tube pass; 4′—distributing tray; 5′,7′—flow-aidingsteam inlet; 6′—lower concentration aqueous phase inlet; 8′—steam inlet;9′—higher concentration aqueous phase outlet.

DETAILED DESCRIPTION OF THE INVENTION

In following descriptions of the process of the present invention,Separation I refers to separating, recovering, and reusing a complexbase catalyst, and separating, recovering, and reusing a powderycomposite catalyst which is optionally at least partially regenerated;Separation II refers to separating, recovering, and reusing aniline, andoptionally separating, recovering, and reusing hydrogenation solvent.

The expression “optionally separating, recovering, and reusinghydrogenation solvent” as used herein means that, when water is used asa hydrogenation solvent, water is optionally recovered and reused, andwhen an alcohol solvent, which will be described herein below, is usedas a hydrogenation solvent, the alcohol hydrogenation solvent isseparated, recovered, and reused.

With reference to FIG. 1, the process for preparing 4-aminodiphenylamineaccording to the present invention comprises the steps of:

-   -   continuously feeding nitrobenzene, aniline and a complex base        catalyst, at desired proportion, to the condensation process        stage reactor via metering pumps, and allowing them to react to        form a condensation liquid (7) containing 4-nitrodiphenylamine,        4-nitrosodiphenylamine and/or salts thereof;

continuously feeding the condensation liquid (7) and hydrogenationsolvent, including supplementary hydrogenation solvent (2) andoptionally recovered hydrogenation solvent (5), at desired proportion tohydrogenation process stage reactor, and allowing them to react withhydrogen gas under the catalytic action of a powdery composite catalyst,including supplementary powdery composite catalyst (1) and reused,optionally regenerated, powdery composite catalyst (4), to form ahydrogenation liquid (8) containing 4-aminodiphenylamine;

feeding the hydrogenation liquid (8) to separation I process stagereactor, where (a) powdery composite catalyst (4), which is to berecycled back to the hydrogenation process stage reactor directly orafter being at least partially regenerated, (b) complex base catalyst(3), which is to be recycled back to the condensation process stagereactor, and (c) aqueous phase obtained by evaporation duringconcentration and organic phase obtained by extraction (9) are obtained;

feeding separately the aqueous phase and the organic phase (9) obtainedin separation I process stage reactor to separation II process stagereactor, where (a) aniline (6), which is to be recycled back to thecondensation process stage reactor, (b) crude 4-aminodiphenylamine fromwhich most aniline has been separated, and (c) optionally, hydrogenationsolvent (5), which is to be recycled back to the hydrogenation processstage reactor, are obtained; and

feeding crude 4-aminodiphenylamine (10) to refining process stagereactor, where (a) partial aniline (6), which is to be recycled back tothe condensation process stage reactor, and (b) finished4-aminodiphenylamine are obtained. The entire process is conductedcontinuously.

(1) Condensation.

In the condensation reaction, the molar ratio of nitrobenzene to anilinemay be in the range of from 1:1 to 1:15. The reaction temperature may bein the range of from 20 to 150° C., preferably from 50 to 90° C. Thereaction temperature is controlled to be no higher than 90° C. in orderto keep the decomposition rate of the complex base catalyst for thecondensation reaction to less than 0.5%. The reaction pressure may varyfrom 0.005 to 0.1 MPa (absolute pressure). The residence time of thefeedstock in the entire condensation reactor is in the range of from 3.5hours to 6 hours.

The complex base catalyst for the condensation reaction comprisestetraalkyl ammonium hydroxide, alkali metal hydroxide, and tetraalkylammonium salt. The complex base catalyst optionally comprises water. Thetotal concentration of tetraalkyl ammonium hydroxide, alkali metalhydroxide, and tetraalkyl ammonium salt is in the range of from 10 to100 percent by weight, preferably from 25 to 38 percent by weight, andthe molar ratio of tetraalkyl ammonium hydroxide to alkali metalhydroxide to tetraalkyl ammonium salt is (0-9):(0.5-3):(0.5-3). Thecombination of tetraalkyl ammonium hydroxide with inexpensive alkalimetal hydroxide or oxide and tetraalkyl ammonium salt can achieve thesame goal as those obtained in the prior art where highly purifiedtetraalkyl ammonium hydroxide alone is used as catalyst. In thecondensation reaction mixture, the molar ratio of hydroxide ion incomplex base catalyst to nitrobenzene is in the range of from 1:4 to4:1.

The complex base catalyst used in the condensation reaction is preparedas follows: tetraalkyl ammonium hydroxide, alkali metal hydroxide oroxide, and tetraalkyl ammonium salt, at desired molar ratio, are stirredin water at a temperature of from 0 to 90° C. until being homogeneous,to form an aqueous form of the complex base catalysts. Then water can becompletely removed by adding benzene through azeotropic process, to forman anhydrous form of the complex base catalyst. The tetraalkyl ammoniumhydroxide, alkali metal hydroxide or oxide, and tetraalkyl ammonium saltas raw materials may be in solid form or in aqueous solution form.

The complex base catalyst used in the present invention is particularlyadvantageous for carrying out the reaction, because the catalyst doesnot need to be constantly replenished. In the course of industrialproduction, the condensation reaction mixture unavoidably contacts withcarbon dioxide and carbon monoxide which are present in both ambient airand hydrogen, which causes tetraalkyl ammonium hydroxide to be convertedto tetraalkyl ammonium carbonate and decrease in the amount. In the casethat only tetraalkyl ammonium hydroxide is used as the catalyst, theconversion of tetraalkyl ammonium hydroxide to ammonium salt decreasesthe quantity of the catalyst so that there is a constant need to supplythe catalyst and get rid of the ammonium salt. In contrast, the presentinvention does not need any complex technology to supply tetraalkylammonium hydroxide and remove ammonium salt. The present inventionprovides that by increasing the contents or ratio of the alkali metalhydroxide or oxide in the complex base catalyst, the complex basecatalyst retains the high catalytic reactivity in the presence of carbondioxide and carbon monoxide during the reaction.

According to the present invention, nitrobenzene and aniline arecondensed to form 4-nitrodiphenylamine and 4-nitrosodiphenylamine and/ortheir salts using the complex base catalyst at certain conditions.Anhydrous complex base catalyst may be used to convert nitrobenzene andaniline to 4-nitrodiphenylamine and 4-nitrosodiphenylamine and/or theirsalts in the condensation reaction according to the present invention.The selectivity and conversion of the reaction attain to the desiredlevel at an anhydrous condition.

By using the complex base catalyst disclosed in the present invention,it is possible to avoid tight control of the proton materials, such aswater, methanol, and the like, in the mixture, thus avoiding as much aspossible the loss of the complex base catalyst and operation complexitydue to the tight control of the proton materials. Without limited to anyspecific theory, it is believed that the integrated action of tetraalkylammonium hydroxide, alkali hydroxide, and tetraalkyl ammonium salt inthe complex base catalyst gives such a result, thereby reducing thedifficulty of operating and controlling the reaction. It is believedthat the use of the complex base catalyst comprising tetraalkyl ammoniumhydroxide, alkali hydroxide, and tetraalkyl ammonium salt makes thecontrol of proton materials, for example water, in the reaction systemunimportant. That is to say, condensation reaction can be carried outand the conversion and selectivity are not affected no matter whetherthere are no proton materials such as water in the solution or there arehigh contents of proton materials such as water in the solution. Thus,the difficulty of operating and controlling the reaction can be reducedand quantity of aniline entrained out by azeotropic dehydration can bedecreased, so that the process is more suitable for industrial scaleproduction.

In the process according to the present invention, the proton materialssuch as water no longer constitute a restricting factor of the reaction,and the selectivity and conversion can attain the desired level whetheror not there are proton materials such as water. Furthermore, it hasbeen found that the decomposition ratio of the complex base catalyst islower than that of the single tetraalkyl ammonium hydroxide being used.

In a preferred embodiment of the present invention, condensationreaction can be carried out in a falling film reactor. In the reaction,nitrobenzene, aniline, and the complex base catalyst in desiredproportion are continuously fed to a falling film reactor via a meteringpump to be heated and allowed to condense. The condensation liquid inthe falling film reactor is discharged from the bottom of the reactorinto a first reactor to continue condensation reaction. A part of thecondensation liquid from the bottom of the first reactor is conveyedback to the falling film reactor via a circulating pump to establish alocal circulating system of the condensation reaction according to thepresent invention. The circulating system is mainly consisted of thefalling film reactor and the first reactor, and the reactantscontinuously circulate via the condensation circulating pump. Thecirculating process maintains a level of condensation liquid that issufficient to form a uniform film in the falling film reactor. Thefalling film reactor may utilize ethanol vapor, hot water, steam ormethanol vapor, preferably ethanol vapor as heat medium, to make thetemperature of the system very homogeneous and avoid local overheating.That there is hardly back-mixing of reaction liquid in the falling filmreactor significantly decreases the chance of contact between thereaction product and the raw materials and minimizes the side reactions.The local circulating system including the falling film reactor enhancesthe condensation reaction rate and reduces the reaction time, which isshortened from more than ten hours to 3.5-6 hours.

It has also been found that continuous film reaction is higher thancomplete mixing reaction in both selectivity and yield. During thisreaction, nitrobenzene reacts with aniline to form4-nitrosodiphenylamine, nitrobenzene can also react with4-nitrosodiphenylamine to form 4-nitrodiphenylamine, and nitrobenzeneitself is reduced to nitrosobenzene, which in turn can react withaniline to form azobenzene. The latter reaction goes against mainreaction and reduces the selectivity of the reaction. At the beginningof reaction, the quantity of nitrobenzene is relatively higher.Nitrobenzene is gradually converted to 4-nitrosodiphenylamine and thequantity of nitrobenzene becomes lower along with the reaction. The useof the continuous falling film reactor reduces the contact and reactionbetween nitrobenzene added and 4-nitrosodiphenylamine which is laterformed (when the reactants enter the reactor to react, the concentrationof nitrobenzene is relatively higher yet the concentration of4-nitrosodiphenylamine is relatively lower, while at the end of thereaction, the concentration of 4-nitrosodiphenylamine is relativelyhigher yet the concentration of nitrobenzene is relatively lower), aswell as the opportunity that nitrobenzene is reduced to nitrosobenzeneby 4-nitrosodiphenylamine, thereby reducing reaction betweennitrobenzene and aniline to form azobenzene.

In the condensation reaction of nitrobenzene and aniline in the presenceof the complex base catalyst, the main side reaction is formation ofby-products, azobenzene and phenazine. It is found that the higher thequantity of aniline, the less the side reaction to convert nitrobenzeneto phenazine. Another by-product in the reaction is azobenzene.Azobenzene can be easily transformed into aniline at the hydrogenationprocess stage, so that it can be reused in the production. Therefore,the molar ratio of nitrobenzene to aniline used in the invention isselected as from 1:1 to 1:15.

Furthermore, in the process of the present invention, condensationreaction can be performed under proper ratio of nitrobenzene and anilinewithout the introduction of any solvent into the system and a good yieldcan be achieved.

The present invention improves the yield of the condensation reactionand makes the reaction moving towards desired direction utilizing theabove method.

Those skilled in the art can contemplate that the condensation reactionaccording to the present process might employ multiple stages ofreactors in series.

In the condensation process stage, it is unavoidable to lose part of thecomplex base catalyst along with the reaction. It is possible to supplyonly alkali metal hydroxide component and tetraalkyl ammonium saltcomponent of the complex base catalyst when replenishing the catalyst,and their molar ratio is in the range of from 4:1 to 1:4. Alkali metaloxide can be used to replace alkali metal hydroxide, and its amount canbe gotten by conversion of corresponding hydroxide to oxide.

The tetraalkyl ammonium salts useful in the present invention can berepresented by a general formula of[(R1)(R2)(R3)(R4)N]⁺ _(n)X^(n−)

wherein R1, R2, R3 and R4, which may be identical or different, can bealkyl having from 1 to 4 carbon atoms, said alkyl can carry ahydrophilic substitute selected from the group consisting of hydroxy,methoxy, polyether, cationic polyamide, polyester, polyethylenepolyamine, highly water-soluble quaternary ammonium salt-containingradical, etc., X^(n−) is selected from the group consisting of halideion, sulfate radical, carbonate radical, phosphate radical, bicarbonateradical, bisulfate radical, C₁-C₂-alkyl carbonate radical, C₁-C₂-alkylsulfate radical, etc., and n is a value of from 1 to 2. Examples of thetetraalkyl ammonium salts include, but not limited to, poly-methylatedtriethylene tetraamine sulfate, poly-methylated diethylene triaminecarbonate, N,N-dimethyl-N,N-bis(methoxyethyl)ammonium carbonate,N-methyl-N,N,N-tri(methoxyethyl)ammonium carbonate,N,N,N-trimethyl-N-hydroxyethyl ammonium carbonate, trimethylhydroxyethyl ammonium chloride, N,N,N-trimethyl-N-ethoxylated(1-4 molesof ethylene oxide)ethyl ammonium carbonate,N,N,N-trimethyl-N-ethoxylated(1-4 moles of ethylene oxide)propylammonium carbonate, N,N,N-trimethyl-N-ethoxylated(1-4 moles of ethyleneoxide)propyl ammonium chloride, N,N-dimethyl-N,N-bis(ethoxylated(1-4moles of ethylene oxide)propyl)ammonium carbonate, tetramethyl ammoniumcarbonate, tetramethyl ammonium methyl-carbonate, tetraethyl ammoniumcarbonate, tetraethyl ammonium ethyl-carbonate, tetramethyl ammoniumsulfate, tetramethyl ammonium methyl-sulfate, tetraethyl ammoniumsulfate, and tetraethyl ammonium ethyl-sulfate.

The tetraalkyl ammonium hydroxide used in the complex base catalyst canbe represented by a formula ofR′₄N⁺OH⁻,

wherein R′ is independently an alkyl having one or two carbon atoms. Thetetraalkyl ammonium hydroxide may be prepared from correspondingtetraalkyl ammonium salt and base in polar solvent according to aprocess known per se.

The alkali metal hydroxides or oxides include hydroxides and oxides oflithium, sodium, potassium and rubidium, such as sodium hydroxide,potassium hydroxide, lithium hydroxide, sodium oxide or potassium oxide.

The tetraalkyl ammonium alkyl-carbonates or tetraalkyl ammoniumalkyl-sulfates useful in the present invention can be prepared by thereaction of trialkyl amine and dialkyl (C₁-C₂) carbonate ordialkyl(C₁-C₂) sulfate in polar solvent.

According to the present invention, the reaction temperature for thepreparation of tetraalkyl ammonium alkyl-carbonate or tetraalkylammonium alkyl-sulfate varies from 50 to 200° C., preferably from 60 to150° C., and reaction pressure varies from 0.1 to 3 MPa (gaugepressure). In general, the pressure depends on the selected temperature,type and amount of the solvent, namely, the less the amount of solvent,the higher the system pressure; and the higher the temperature, thehigher the pressure. In the invention, the reaction pressure ispreferably controlled in a range of from 0.4 to 2 MPa to obtain higherproduct yield.

In the reaction for the preparation of tetraalkyl ammoniumalkyl-carbonate or tetraalkyl ammonium alkyl-sulfate according to thepresent invention, the molar ratio of trialkyl amine to dialkyl(C₁-C₂)carbonate or dialkyl(C₁-C₂) sulfate is selected as from 2:1 to 1:2. Ifthe proportion of trialkyl amine is too high, then trialkyl amine willbe superabundant in the reaction system and thus impose operationaldifficulty to subsequent processes and pollutes the environment. If theproportion of trialkyl amine is too low, then dialkyl(C₁-C₂) carbonateor dialkyl(C₁-C₂) sulfate will be superabundant, and thus cause the lossof dialkyl(C₁-C₂) carbonate or dialkyl(C₁-C₂) sulfate in the subsequentreaction, thereby increasing the production cost.

In the process for the preparation of tetraalkyl ammoniumalkyl-carbonate or tetraalkyl ammonium alkyl-sulfate according to thepresent invention, reaction time of trialkyl amine anddialkyl(C₁-C₂)carbonate or dialkyl(C₁-C₂)sulfate is in a range of from1.5 to 6 hours. At the initial stage of the reaction, the reaction rateis high, and exothermic phenomenon is obvious. With consumption of rawmaterials, the reaction slows down and heat release is graduallyreduced. During the reaction, the amount of cooling water iscontinuously adjusted to keep reaction temperature and pressure in acertain range.

The polar solvents useful in the condensation reaction according to thepresent invention include methanol, ethanol, or isopropyl alcohol. Theamount of solvents used varies from 1 to 10 times of weight of trialkylamine.

(2) Hydrogenation.

In the hydrogenation reaction of the present invention, hydrogen gas canbe used as the reducing agent. The reaction temperature is in the rangeof from 50 to 100° C. The reaction pressure is in the range of from 0.2to 3.0 MPa (absolute pressure). The reaction time varies from 2 hours to7 hours. The volume ratio of gas to liquid is in the range of from 10:1to 1500:1; the weight ratio of solid to liquid is in the range of from0.5:100 to 16:100. The gas refers to the hydrogen gas; the liquid refersto the hydrogenation solvent and the condensation liquid; the solidrefers to the powdery composite catalyst.

In the present invention, alcohols and/or water can be used ashydrogenation solvent. Among alcohols, methanol, ethanol, and isopropylalcohol are preferred. The hydrogenation solvent can be used in such anamount that the weight ratio of the hydrogenation solvent to thecondensation liquid is in the range of from 1:10 to 5:10. When analcohol is used as the hydrogenation solvent, the alcohol need to beseparated, recovered, and recycled. When water is used as thehydrogenation solvent, the aqueous phase after extraction as describedherein below, is concentrated to give the complex base catalyst of thepresent invention and the water obtained during the concentration isoptionally recycled to the hydrogenation stage reactor.

The powdery composite catalyst of the present invention is used in thehydrogenation reaction which comprises nickel, aluminum, and componentA. Component A is at least one selected from the group consisting of Fe,Cu, Co, Mn, Cr, Mo, B and P. The amount of nickel is in the range offrom 25 to 99.9 wt %, and the total amount of aluminum and component Ais in the range of from 0.1 to 75 wt %. The particle size of thecatalysts may vary from 40 to 300 mesh.

The component A acts as a modifying agent to modify the crystallinestate of the nickel-aluminum alloy to improve the selectivity of thehydrogenation reaction and enhance the activity of powdery compositecatalyst.

The powdery composite catalyst according to the present invention can beprepared by mixing powdery nickel, powdery aluminum, and component A indesired proportion, then melting them at a high temperature, followed bypulverizing them into powder of from 40 to 300 mesh after dischargingand quenching, and finally, treating the powder with hydroxide aqueoussolution. The concentration of hydroxide can be in the range of from 5to 50 weight percentage. The reaction temperature is 50-90° C.

In order to improve the recovery of the hydrogenation catalyst, thepresent invention provides a magnetic separator coupled with the use ofat least iron as the modifying agent, component A, to increase theferromagnetism of the powdery composite catalysts and recover thepowdery composite catalyst using the ferromagnetism thereof. Therefore,in a preferred embodiment of the present invention, the powderycomposite catalyst of the present invention may be prepared by takingpowdery nickel, powdery aluminum, powdery iron, and optional othermodifying agent A, which is selected from the group consisting of Cu,Cr. Co, Mn, Mo, B and P, in desired proportion; melting them into alloyin an induction furnace; ejecting the molten alloy using gas pressurethrough a nozzle to a copper drum rotating at high speed to quenchquickly the alloy with cooling speed being as high as 10⁵-10⁶K/sec;pulverizing the cooled alloy using a ball mill into powder of from 40 to300 mesh, preferably from 100 to 200 mesh; and finally, treating thepowder with 5 to 50 wt.-% hydroxide aqueous solution at a temperature of50 to 90° C.

According to the preferred embodiment of the present invention,hydrogenation reaction can be carried out as follows: condensationliquid from the previous step, hydrogenation solvent, powdery compositecatalyst recovered and, if necessary, complementary fresh powderycomposite catalyst are fed to first-stage, second-stage, and optionallyhigh-stage hydrogenation reactors by a solid-liquid conveyer, andhydrogen gas is bubbled into the reactors from the bottom of thereactors via a hydrogen gas circulator, to carry out the hydrogenationreaction under the above hydrogenation reaction conditions to form crudehydrogenation liquid containing 4-aminodiphenylamine. The powderycomposite catalyst entrained out by crude hydrogenation liquid isseparated by a settling vessel and a magnetic separator. Solid-liquidphase, which separates from hydrogenation liquid and contains highconcentration of the powdery composite catalyst, enters into the firstreactor to be reused through a mixed solid-liquid conveying device. Atthe same time, hydrogenation liquid containing 4-aminodiphenylamine isobtained.

The powdery composite catalyst according to the present invention is asolid-state material during the hydrogenation. In industry, thehydrogenation catalyst is typically circulated via a pump, however, whena pump is used to convey a catalyst containing a high concentration ofpowdery metal, pump cavity is easily damaged and the transportationeffect is also not good. The present invention provides the use of aVenturi-like solid-liquid conveying device, and circulation of thepowdery composite catalyst in hydrogenation system is achieved through apump-free circulation performed by skillfully employing the power of thepump for feeding condensation solution, so that the loss of catalyst issignificantly reduced, and the concentration of catalyst in condensationsolution is significantly enhanced.

According to a preferred embodiment, in continuous hydrogenationprocess, the powdery composite catalyst in crude hydrogenation liquid isrecovered through sedimentation and magnetic separator and recycled viaVenturi type solid-liquid conveying device, and circulating hydrogen gasis bubbled into the reactors. The whole hydrogenation step is conductedin a complete mixing flow mode by continuously feeding stock intomultistage reactors in series. The hydrogenation solvents can be therecovered and reused.

(3) Separation I.

The hydrogenation liquid having part of the powdery composite catalystrecovered through sedimentation and magnetic separator enters into theseparation I process stage reactor, where the residual powdery compositecatalyst in the hydrogenation liquid is recovered from hydrogenationliquid by filtration, and circulated back to the hydrogenation processstage directly or after being at least partially regenerated.

In the hydrogenation reaction of the present invention, with optionallycontinuously renewing a minor amount of hydrogenation catalyst, thecatalyst concentration in the reaction system can always maintain athigh level. Such a method of recycling catalyst can always and stablymaintain the total activity of catalyst in the system at a higher leveland avoid the problem that catalyst activity gradually decreasessuffered by the processes employing fixed bed catalyst. The use ofmagnetic separator facilitates the recovery of the catalyst, and thedesigning and application of mixed solid-liquid conveying device makespowdery composite catalyst circulating in the hydrogenation system.

In the present invention, deactivation of catalyst is usually caused bythe inorganic matter or organic carbon deposition clog pores of thecatalyst, so that the active sites of the catalyst are covered, andthereby the activity of the catalyst decreases. Therefore, the presentinvention employs washing with a high concentration base solution, forexample, 5-50 wt % aqueous solution of alkali metal hydroxide incombination with ultrasonic oscillation to regenerate the catalyst.Ultrasonic oscillation facilitates to get rid of the inorganic ororganic carbon deposition, while the high concentration base solutioncan dissolve the aluminum, which isn't dissolved in the first basedissolution, in the catalyst to form new loose pore structures, therebyincreasing the activity of the catalyst.

The present invention provides sedimentation and magnetic separator torecover magnetic hydrogenation catalyst, and design a Venturi type mixedsolid-liquid conveying device to convey the catalyst back tohydrogenation reactor using the force of feeding the stocks, therebyachieving the circulation of powdery composite catalyst. The inventorsalso take out the catalyst after filtration to regenerate it to restoreits initial activity. By the two measures, the consumption of catalystis significantly reduced, and the activity and life time of catalyst areimproved.

(4) Separation II.

The filtrate is extracted with extracting agent and co-extracting agentto obtain an organic phase and an aqueous phase. The organic phase isconveyed to separation II process. The aqueous phase is subjected toone-stage or multistage concentration to give the complex base catalystof the present invention, which is recycled back to the condensationprocess.

Specifically, in the practice of the present invention, water is used asan extracting agent and the volume ratio of water to hydrogenationliquid can vary from 0.5:1 to 5:1, preferably from 0.8:1 to 1.2:1.Organic polyethers is used as co-extracting agent, and examplesincludes, but not limited to, polyethylene glycol ethers, such aspolyethylene glycol dimethyl ether having a molecular weight of from 200to 1000, polyethylene glycol diethyl ether having a molecular weight offrom 200 to 1000, and polyethylene glycol methyl ethyl ether having amolecular weight of from 200 to 1000; polypropylene glycol ethers, suchas polypropylene glycol dimethyl ether having a molecular weight of from200 to 1000, polypropylene glycol diethyl ether having a molecularweight of from 200 to 1000, and polypropylene glycol methyl ethyl etherhaving a molecular weight of from 200 to 1000; fatty alcoholpolyoxyethylene ethers, such as those wherein the fatty alcohol has 12to 18 carbon atoms and polymerization degree of polyoxyethylene is from3 to 15. The volume ratio of the co-extracting agent to water is in arange of from 0.0001:1 to 0.005:1. Pressure during extraction can be ina range of from 0.005 to 0.1 MPa, extraction temperature can be in arange of from 0 to 80° C., and extraction time can vary from 2 to 5 h.Supernatant aqueous phase containing hydrogenation solvent and complexbase catalyst and organic phase mainly containing aniline,4-aminodiphenylamine, and a minor amount of organic impurities areobtained after separation.

Concentration of aqueous phase can be conducted using one-stage ormultistage gas-aid falling film evaporator. In general, heat medium usedin the concentration can be water, steam or secondary steam from thepreceding stage evaporator. In the gas-aid falling film evaporator ofthe present invention, shell pass is heated by steam, and another partof steam enters into the tube pass from steam inlet on the top ofone-stage falling film evaporator, namely flow-aiding inlet. Aqueousphase enters into the tube pass from lower concentration aqueous phaseinlet of the gas-aid falling film evaporators. The direction of steammotion is the same as the direction of aqueous phase motion, and thesteam is of an assistant power. Specifically, as shown in FIG. 2, thegas-aid falling film evaporators include shell pass (2′), tube pass(3′), steam inlet (8′) installed on the top of shell pass (2′),condensed water outlet (1′) installed at the bottom of shell pass (2′),lower concentration aqueous phase inlet (6′) installed on the top oftube pass (3′), higher concentration aqueous phase outlet (9′) installedat the bottom of tube pass (3′), flow-aiding steam inlet (5′ and 7′)installed on the top of tube pass (3′) and distributing tray (4′)installed at a position below the lower concentration aqueous phaseinlet (6′).

In the falling film evaporators, the aqueous phase, carried by thesteam, passes through distributing tray and flows in film form from topto bottom in the tubes. The residence time of the aqueous phase iscontrolled in a range of from 2 to 60 seconds and the temperature of theaqueous phase can be in a range of from 30 to 105° C. The pressure ofshell pass steam used in the concentration is in a range of from 0.005to 0.1 MPa (absolute pressure). With the use of a gas-aid falling filmevaporator and utilizing the steam to carry the aqueous phase flowingfrom the top to the bottom, the liquid flow rate is quickened and theresidence time is controlled, at the meantime, low-boiling substances inthe aqueous phase is largely evaporated at the higher temperature. Thusthe decomposition of complex base catalyst containing tetraalkylammonium hydroxide can be minimized. If the hydrogenation solvent is analcohol, the condensate from the condensation of evaporated substanceswhich is a mixture of water and the alcohol can be conveyed toseparation II process to recover the hydrogenation solvent. If thehydrogenation solvent is a mixture of water and an alcohol, thecondensate from the condensation of evaporated substances which is amixture of water and the alcohol can be recycled back to thehydrogenation process or conveyed to separation II process to recoverthe alcohol. If the hydrogenation solvent is water, the condensate fromthe condensation of evaporated substances which is water can be recycledback to the hydrogenation process.

In the separation II process stage of the present invention, aniline isobtained by evaporation from the extracted organic phase conveyed fromseparation I process stage, and the aniline is recycled back to thecondensation process. The column bottoms from which most aniline isseparated are conveyed to refining process. The operating pressure ofthe evaporator can vary from 0.005 to 0.1 MPa (absolute pressure),column bottom temperature is in a range of from 120 to 320° C., and thetemperature of gas phase is in a range of from 60 to 190° C.

In the cases where the hydrogenation solvent is an alcohol or a mixtureof an alcohol and water, the evaporator condensate which is obtainedfrom the condensation of aqueous phase in separation I process issubjected to rectification to give the alcohol as hydrogenation solvent,and the alcohol is recycled back to the hydrogenation process.

(5) Refining.

The organic phase having most aniline separated in separation II processstage contains 4-aminodiphenylamine, aniline, azobenzene and phenazine,etc. In an embodiment of the present invention, the refining process isconducted through three-column continuous rectification and batchrectification, wherein the organic phase to be refined is conveyed via apump into rectification column 1, where aniline, azobenzene andphenazine are taken out from the column top, and crude4-aminodiphenylamine is discharged from the column bottom. The effluentfrom the top of rectification column 1 enters into rectification column3, where aniline with a purity of about 99% is distilled from the top ofrectification column 3 and can be directly recycled back to condensationprocess, and azobenzene and phenazine are left in the column bottom.Column bottoms of rectification column 1 are conveyed via a pump torectification column 2, where the finished 4-aminodiphenylamine isdistilled from the top of rectification column 2, and column bottoms ofrectification column 2, after accumulating to a certain amount, areconveyed to batch still, where a minor amount of 4-aminodiphenylamineleft in the bottoms is distilled off and conveyed back to rectificationcolumn 2, and the other residues are discharged from the still bottom.

In the above refining process according to the present invention, therectification column 1 is operated at a vacuum degree of from 0.09 to0.098 MPa, a reflux ratio of from 2:1 to 10:1, a column top temperatureof from 80 to 130° C., a still temperature of from 260 to 290° C.; therectification column 2 is operated at a vacuum degree of from 0.09 to0.098 MPa, a reflux ratio of from 1:0.5 to 1:4, a column top temperatureof from 140 to 190° C., a still temperature of from 260 to 300° C.; therectification column 3 is operated at a vacuum degree of from 0.09 to0.098 MPa, a reflux ratio of from 1:0.5 to 1:2, a column top temperatureof from 80 to 120° C., a still temperature of from 120 to 170° C.; andthe batch rectification column is operated at a vacuum degree of from0.09 to 0.098 MPa, a column top temperature of from 235-250° C., and astill temperature of from 280 to 330° C. The still temperature of therectification column 2 is relatively lower, thus coking of4-aminodiphenylamine can be reduced, and 96% or more of4-aminodiphenylamine can be distilled off at the top of rectificationcolumn 2 operated at a relatively lower still temperature, so that theamount of 4-aminodiphenylamine in the bottoms to be subjected to batchevaporation is significantly reduced.

In the process for preparing 4-aminodiphenylamine according to thepresent invention, the complex base catalyst and powdery compositecatalyst used have lower production cost and higher catalytic activity;the whole process can be continuously carried out and is suitable forindustrial scale production; the use of the complex base catalysts incondensation process significantly decreases the difficulty of operatingand controlling the reaction and renders the water in the reactionsystem being no longer a reaction-confining factor; the decomposition ofcomplex base catalyst is much less than that of the single tetraalkylammonium hydroxide catalyst; the selection of a falling film reactor andraw material proportion improves selectivity of the reaction; thereneeds no solvent; the hydrogenation reaction can be carried out at alower temperature and mild reaction conditions, and the hydrogenationcatalyst is good at antitoxic performance, by-product is little, andconversion and selectivity is high; a magnetic separator is used torecover magnetic powdery composite catalyst during hydrogenationprocess; the hydrogenation catalyst is conveyed back to hydrogenationreactor via a Venturi type mixed solid-liquid conveying device using theforce of feeding stocks; catalyst can be regenerated by chemical and/orphysical methods, and thus the consumption of catalyst is reduced; thecomplex base catalyst is recovered after hydrogenation, and watercontaining co-extracting agent is used as extracting agent to separatethe complex base catalyst; the aqueous phase is concentrated byone-effect or multi-effect gas-aid falling film evaporator to recoverthe complex base catalyst; the whole process is continuous and theoperational strength is low; no corrosive liquid is produced, andenvironment pollution is almost eliminated. The purity of4-aminodiphenylamine can exceed 99 wt %, and the yield in the wholeindustrial production process can be over 95 wt %.

EXAMPLES

The following examples further describe the present invention, but donot make limitation to the scope of the present invention in any way.

Example 1 Preparation of a Complex Base Catalyst

To a 1000 ml three-necked flask equipped with a condenser and a stirrerwere added 227.5 g of 20 wt.-% aqueous solution of tetramethyl ammoniumhydroxide (0.5 mol), 10 g (0.25 mol) of sodium hydroxide and 346 g of 30wt.-% aqueous solution of tetramethyl ammonium carbonate (0.5 mol). Themixture was homogeneously stirred at 72-77° C. to give a complex basecatalyst having a concentration of 27.3 wt.-%.

Example 2 Preparation of a Powdery Composite Catalyst

46 g of powdery nickel, 51 g of powdery aluminum, and 3 g of powderyiron were taken and mixed, then molten into alloy state in an inductionfurnace. The molten alloy was ejected using gas pressure through anozzle to a copper drum rotating at high speed to be quenched quicklywith cooling speed being as high as 10⁵-10⁶K/sec. The cooled alloy waspulverized using a ball mill, and 99.7 g of powder of from 40 to 300mesh were obtained by sieving. 375 g of 20 wt.-% sodium hydroxideaqueous solution was charged into a 500 ml three-necked flask equippedwith a thermometer and a stirrer, and the above powder is slowly addedthereto. The mixture was stirred at 60° C. for 4 h, then the solid waswashed with deionized water until neutral to give a powdery compositecatalyst.

Example 3

Under vacuum condition, feeding pumps of the above complex basecatalyst, aniline and nitrobenzene were simultaneously switched on andadjusted to such flow rate as aniline 150 kg/h, nitrobenzene 30 kg/h andthe complex base catalyst 200 kg/h. The aniline, nitrobenzene andcomplex base catalyst were continuously fed into a falling film reactorto be heated and allowed to condense. Condensation liquid in the fallingfilm reactor was discharged from the bottom into a first reactor toproceed with condensing. Part of condensation liquid from the bottom ofthe first reactor was conveyed back to the falling film reactor via acirculating pump, forming a local circulating system. Ethanol vapor at78-90° C. was used as the heat medium of the falling film reactor.Reaction temperature was controlled as 75° C., pressure was controlledas 0.008 MPa (absolute pressure) and flow rate of the circulating liquidwas controlled as 1 m³/h. The reactants overflowed from the firstreactor into a second-stage reactor. The process conditions of thesecond-stage reactor, such as operational temperature and pressure, wereidentical with that of the first reactor. The total residence time ofthe reactants in the falling film reactor, first reactor andsecond-stage reactor was controlled as 5 h. Once the condensationreaction became stable, the complex base catalyst recovered according tothe procedure as described in the following examples could be used, withonly a minor amount of fresh complex base catalyst prepared according toexample 1 being replenished, so that the molar ratio of hydroxide ion tonitrobenzene was controlled not less than 1:1. The effluent of thesecond-stage reactor was found to contain not larger than 0.1 wt.-% ofnitrobenzene, 24.9 wt.-% of water and 16.1 wt.-% of4-nitrosodiphenylamine and 4-nitrodiphenylamine.

Example 4

Under vacuum condition, feeding pumps of the complex base catalyst,aniline and nitrobenzene were simultaneously switched on and adjusted tosuch flow rate as aniline 150 kg/h, nitrobenzene 30 kg/h and the complexbase catalyst 200 kg/h. The aniline, nitrobenzene and complex basecatalyst were continuously fed into a falling film reactor to be heatedand allowed to condense. Condensation liquid in the falling film reactorwas discharged from the bottom into a first reactor to proceed withcondensing. Part of condensation liquid from the bottom of the firstreactor was conveyed back to the falling film reactor via a circulatingpump, forming a local circulating system. Ethanol vapor at 78-90° C. wasused as the heat medium of the falling film reactor. Reactiontemperature was controlled as 75° C., pressure was controlled as 0.008MPa (absolute pressure) and flow rate of the circulating liquid wascontrolled as 1 m³/h. The reactants overflowed from the first reactorinto a second-stage reactor. The process conditions of the second-stagereactor, such as operational temperature and pressure, were identicalwith that of the first reactor. The total residence time of thereactants in the falling film reactor, first reactor and second-stagereactor was controlled as 5 h. Once the condensation reaction becamestable, the complex base catalyst recovered was used, with sodiumhydroxide and tetraalkyl ammonium salt (i.e. tetramethylammniumcarbonate according to Example 1) in a molar ratio of 1:1 beingreplenished, so that the molar ratio of hydroxide ion to nitrobenzenewas controlled not less than 1:1. The effluent of the second-stagereactor was found to contain not larger than 0.1 wt.-% of nitrobenzene,15.6 wt.-% of water and 17.6 wt.-% of 4-nitrosodiphenylamine and4-nitrodiphenylamine.

Example 5 Hydrogenation

The condensation liquid as prepared in Example 3 was conveyed tohydrogenation reactor after filtration. Hydrogen gas was used to replacethe atmosphere of the system and pressurize to 1.3 MPa. A hydrogen gascirculator was switched on and flow rate of circulating hydrogen gas wasmaintained at 1 Nm³/h. The circulating hydrogen gas was bubbled into thehydrogenation reactor to improve the gas-liquid mass transfer effectduring reaction. The flow rate of condensation liquid of nitrobenzeneand aniline was controlled as 306 kg/h, and the flow rate of methanolwas controlled as 601/h (48 kg/h). The hydrogenation feedstock was fedinto a first-stage hydrogenation reactor equipped with a sealed magneticstirrer and a cooling and heating system, and powdery composite catalystabove prepared was added simultaneously so that the solid-liquid ratioby weight was 6:100. Hydrogenation-reduced liquid overflowed from thefirst reactor into a second-stage reactor, then into a third-stagereactor, finally into a settler. The reaction temperature was 75-80° C.,pressure was 1.3 MPa and total residence time was 5 h. The powderycomposite catalyst was recovered as much as possible under the action ofa magnetic separator. Solid-liquid mixture containing higherconcentration of solid catalyst at the bottom of the settler wasreturned to the first-stage hydrogenation reactor via a Venturi typesolid-liquid conveying device using the force of feeding stocks. Theactivity of the catalyst in the hydrogenation reaction was judged bymonitoring the endpoint of reducing reaction, and thus it could bedetermined whether powdery composite catalyst for hydrogenation reactionwas replenished.

The hydrogenation-reducing liquid was measured by high performanceliquid chromatograph (HPLC) and was found not containing4-nitrodiphenylamine and 4-nitrosodiphenylamine.

Example 6 Separation I

The hydrogenation liquid as prepared in Example 5, after settling andmagnetic separating the powdery composite catalyst, was subjected tofiltration to recover extremely fine powdery composite catalyst whichwas not recovered by magnetic separation. The powdery composite catalystrecovered by filtration was recycled back to the hydrogenation processafter regeneration.

Hydrogenation-reduced liquid containing no solid catalyst wascontinuously fed at a flow rate of 3601/h to top of an extraction columnvia a metering pump, and extracting agent water having the same flowrate of 3601/h and co-extracting agent polyethylene glycol dimethylether with a molecular weight of 400-800 having a flow rate of 0.41/hwere continuously fed to the bottom of the extraction column. Afterextraction, aqueous phase was discharged from the column top and organicphase was discharged from the column bottom. The extraction time was 3 hand extraction pressure was atmospheric pressure. Methanol and thecomplex base catalyst in the hydrogenation-reduced liquid were extractedby water to aqueous phase. An aqueous phase was obtained at an amount of5401/h and organic phase was obtained at an amount of 1801/h.

The aqueous phase, after preheated to 80° C., was fed at a flow rate of5401/h via a metering pump to top of a gas-aid falling film evaporatorwhose shell pass was heated with 120° C. steam. The residence time ofthe stuff in the evaporator was 10 sec. The primary concentrated liquidwas conveyed to a second-stage shell-and-tube falling film evaporatorunder 0.1 MPa (absolute pressure) and the residence time of the stuff inthis evaporator was 10 sec. The temperature of gas-liquid mixturedischarged from second-stage falling film evaporator was 80-95° C. Afterseparating via secondary gas-liquid separator, recovery ratio of thecomplex base catalyst in the whole concentrating process might be ashigh as 99.7%. The complex base catalyst was recycled back to thecondensation process.

Example 7 Separation II

The gas phase evaporated from the falling film evaporators condensed togive a methanol-water solution containing about 28 wt. % of methanol.The methanol-water solution was continuously pumped to a rectificationcolumn to conduct separation, thus methanol having a purity of more than99 wt. % was obtained from column top and could be reused in thehydrogenation process, and water was in the column bottom. The water inthe column bottom was measured by gas chromatography (GC) and it wasfound that the content of methanol therein was less than 0.3 wt. %

The organic phase from extraction operation was fed to a shell-and-tuberising film evaporator to separate most aniline. Operational pressure ofthe rising film evaporator was 0.01 MPa (absolute pressure), and 180° C.steam was used to heat in the shell pass. A gas phase at 75-105° C. anda liquid phase at 160° C. were gained from a gas-liquid separatorlocated on the top of the rising film evaporator. The gas phase materialafter condensation was measured by chromatography and the content ofaniline was found as high as 99 wt. %. Most of aniline was distilledduring the process, and the distilled aniline could be recycled back tothe condensation process as the raw material of condensation reaction.Liquid phase material was the crude product of 4-aminodiphenylamine,containing 78.1 percent of 4-aminodiphenylamine, 21.75 percent ofaniline and the balance amount of other organic impurities.

Example 8 Refining

The crude product of 4-aminodiphenylamine (containing 78.1%4-aminodiphenylamine, 21.75% aniline, 0.05% azobenzene, and 0.1%phenazine) was continuously fed to rectification column 1 at a flow rateof 120 kg/h via a gear pump. The temperature of still was controlled as270° C., the temperature of column top was controlled as 110° C., vacuumdegree was controlled as 0.094 MPa and reflux ratio was controlled as5:1. Light components, i.e. aniline, azobenzene and phenazine, weretaken out from the column top at a flow rate of about 26.2 kg/h, andconveyed to rectification column 3.

The rectification column 3 was operated at conditions of stilltemperature of 150° C., column top temperature of 90° C., vacuum degreeof 0.094 MPa and reflux ratio of 1:1. Aniline was distilled off fromcolumn top at a flow rate of 24 kg/h, and azobenzene and phenazine wereleft in column bottom.

Column bottoms of the rectification column 1 were conveyed torectification column 2. The rectification column 2 was operated atconditions of still temperature of 280° C., column top temperature of170° C., vacuum degree of 0.097 MPa and reflux ratio of 1:1. Thefinished 4-aminodiphenylamine was obtained at the column top of therectification column 2.

Column bottoms of the rectification column 2 were conveyed to batchstill. The batch still was operated at conditions of kettle temperatureof 285-320° C., vacuum degree of 0.094 MPa and top temperature of235-250° C., to distill off the residual 4-aminodiphenylamine, which wasrecycled back to the rectification column 2 to be further distilled. Thewhole refining process of 4-aminodiphenylamine was continuously carriedout. The finished 4-aminodiphenylamine product obtained had a purity of99.1%, a melting point of 72° C. and a solidifying point of 72.4° C. Theyield of the process step in industrial production was 95.1%.

Example 9 Process for Regenerating Catalyst

20 g of powdery composite catalyst, which was recovered by filtration ofthe hydrogenation liquid, was charged into a 100 ml three-necked flaskequipped with a stirrer and a thermometer. 20 ml of 40% aqueous solutionof sodium hydroxide was added thereto. While stirring, the mixture washeated to 90° C. and maintained at that temperature for 1 h. At the endof the reaction, the catalyst was subjected to ultrasonic washing for 30min in a washing tank, followed by washing with water for multiple timesuntil the pH of the washing water was 7-8. The gained solid wasregenerated powdery composite catalyst.

Example 10 Preparation of a Complex Base Catalyst

To a 500 ml three-necked flask equipped with a condenser and a stirrerwere added 230 g of water, followed by adding 91 g of pentahydratedtetramethyl ammonium hydroxide (containing 0.5 mol of tetramethylammonium hydroxide), 20 g (0.5 mol) of sodium hydroxide and 70 g oftrimethylhydroxyethyl ammonium chloride (0.5 mol). The mixture washomogeneously stirred at 75±2° C. to give a complex base catalyst havinga concentration of 32.85 wt.-%.

Example 11 Preparation of a Complex Base Catalyst

To a 500 ml three-necked flask equipped with a condenser and a stirrerwere added 230 g of water, followed by adding 91 g of pentahydratedtetramethyl ammonium hydroxide (containing 0.5 mol of tetramethylammonium hydroxide), 20 g (0.5 mol) of sodium hydroxide and 74.5 g oftetramethyl ammonium methylcarbonate ([(CH₃)₄N]⁺[CO₃CH₃]⁻)(0.5 mol). Themixture was homogeneously stirred at 75±2° C. to give a complex basecatalyst having a concentration of 33.7 wt.-%.

Example 12

To a 500 ml four-necked flask equipped with a stirrer and a watersegregator and a condenser were added 150 g of water, followed by adding91 g of pentahydrated tetramethyl ammonium hydroxide (containing 0.5 molof tetramethyl ammonium hydroxide), 20 g (0.5 mol) of sodium hydroxideand 74.5 g of tetramethyl ammonium methylcarbonate([(CH₃)₄N]⁺[CO₃CH₃]⁻)(0.5 mol). Then 25 g of benzene were added thereto,and the mixture was heated to reflux. There were water layer and oillayer in the water segregator. Oil layer was returned to the four-neckedflask and water layer was separated out until there was no water indistilled liquid. An anhydrous form of complex base catalyst wasobtained.

Example 13 Preparation of Tetramethylammonium Methyl-Carbonate([(CH₃)₄N]⁺[CO₃CH₃]⁻)

To a 1.5 L autoclave equipped with a stirrer and a heating means wereadded 90 g (1.0 mol) of dimethyl carbonate, 59 g (1.0 mol) of trimethylamine and 510 g (15 mol) of methanol. Stirring was initiated after theautoclave was sealed. The autoclave was heat to 140° C., and pressurewas 1.5 MPa. The reaction was kept at 140° C. for 4 h. Then the reactionmixture was cooled to 50° C. and discharged into a 1 L three-neckedflask. Part of methanol was removed from the solution oftetramethylammonium methyl-carbonate in methanol thus obtained undervacuum, and then the solution was cooled to ambient temperature. Whitecrystal precipitated out. The crystal was filtrated, oven dried andrecrystallized from methanol, to give 119.5 g of tetramethylammoniummethyl-carbonate having a purity of 99.2% as measured by chromatography.The yield was 80.2%.

Example 14

92.5 g (1 mol) of 1-chloro-2,3-epoxy propane, 3 g (1 mol) of N-methyldiethanolamine, 2 g of sodium hydroxide and 700 g of water were chargedinto an autoclave with a stirrer, a heating means and a thermometricmeans. With stirring, the mixture was gradually heated to 120° C., thengaseous ethylene oxide was continuously passed into the autoclave tomaintain a reactor pressure of 0.3 MPa until the quantity of ethyleneoxide passed into reached 150 g. The reaction continued for further 2 hat that temperature, to give ClCH₂[CH₂CH₂O]₂₋₅—H. 60 g of gaseoustrimethylamine were passed thereto. The autoclave was heat to 140° C.,and pressure was 1.5 MPa. The reaction was maintained at thattemperature for 4 h. Then the mixture was cooled to room temperature.After conventionally dehydrating and drying, 105 g ofN,N,N-trimethyl-N-ethoxylated(1-4 moles of ethylene oxide)propylammonium chloride was obtained.

Example 15 Preparation of Tetramethyl Ammonium Hydroxide

To a 1.5 L autoclave equipped with a stirrer and a heating means wereadded 90 g (1.0 mol) of dimethyl carbonate, 59 g (1.0 mol) of trimethylamine and 510 g (15 mol) of methanol. Stirring was initiated after theautoclave was sealed. The autoclave was heated to 140° C., and pressurewas 1.5 MPa. The reaction was kept at 140° C. for 4 h. Then the reactionmixture was cooled to room temperature and discharged into a 1 Lthree-necked flask. A slurry consisting of 148 g (2.0 mol) of calciumhydroxide and 350 g of water was added thereto. Methanol was distilledoff by heating over 8 h while stirring. 355 g of tetramethyl ammoniumhydroxide solution was obtained after filtration. The content oftetramethyl ammonium hydroxide was found as 24.4% and the total reactionyield was 95.2%.

Example 16 Preparation of Tetraethyl Ammonium Hydroxide

To a 1.5 L autoclave equipped with a stirrer and a heating means wereadded 154 g (1.0 mol) of diethyl sulfate, 101 g (1.0 mol) of triethylamine and 690 g (15 mol) of ethanol. Stirring was initiated after theautoclave was sealed. The autoclave was heat to 140° C., and pressurewas 1.0 MPa. The reaction was kept at 140° C. for 4 h. Then the reactionmixture was cooled to room temperature and discharged into a 1 Lthree-necked flask. 80 g (2.0 mol) of sodium hydroxide was addedthereto. The reaction mixture was heated to 45° C. for 4 h whilestirring. After filtration, part of ethanol was distilled off from thefiltrate. Then 500 g of water was added while ethanol was distilled off(part of water was entrained out), to give 604 g of tetraethyl ammoniumhydroxide solution. The content of tetraethyl ammonium hydroxide wasfound as 23.3 wt.-% and the total reaction yield was 95.7%.

Example 17 Effect on Reaction Imposed by the Quantity of Aniline andNitrobenzene

A local circulating system having a total volume of 1 L was comprised ofa miniature reactor equipped with a vacuum system and a temperaturecontrol system, a film reactor and a circulating pump. The system wasfirstly filled with aniline, and the flow of the circulating pump wasset at 2 1/h. A mixture, containing nitrobenzene, aniline and thecomplex base catalyst prepared according to example 1 at a molar ratioof nitrobenzene to aniline to OH⁻ in the complex base catalyst of1:1:1.8, was fed to the reactor at a flow rate of 200 ml/h. Theresidence time was 5 h. The system temperature was maintained as 75° C.and the system pressure was maintained as 0.008 MPa (absolute pressure).After the aniline was replaced by reaction liquid and reaction liquidwas stable in composition, a sample was taken and analyzed. Nitrobenzenewas substantially not detectable. The reaction selectivity wascalculated according to the total mole number of 4-nitrosodiphenylamineand 4-nitrodiphenylamine generated.

The results obtained under the same conditions except that the ratio ofnitrobenzene to aniline was changed were showed in table 1. TABLE 1Effect On Reaction by Quantities Of Aniline And NitrobenzeneNitrobenzene:aniline Reaction selectivity No. (mol/mol) (%) 1 1:1 90.2 21:3 96.1 3 1:5 99.1 4  1:10 99.3

It can be seen from the data showed in table 1 that increasing the molarratio of aniline to nitrobenzene will enhance the reaction selectivity,increase target products and reduce the by-products. However, in thepractice, if the quantity of aniline is too large, the loss of anilineand the energy consumption during separation will increase.

Example 18 Effect on Condensation Reaction Imposed by Water

A continuous reactor was connected to a vacuum system and equipped witha temperature control system, and formed a local circulating system witha falling film evaporator and a circulating pump. Total volume of thereaction system was 1 L. The system was firstly filled with aniline, andthe flow of the circulating pump was set at 21/h. A mixing liquidcontaining nitrobenzene, aniline and the complex base catalyst at amolar ratio of nitrobenzene to aniline to OH⁻ in the complex basecatalyst of 1:7:1.15 was fed to the reactor at a certain flow. Thesystem temperature was maintained as 75° C. and the system pressure wasmaintained as 0.008 MPa (absolute). After the aniline was replaced byreaction liquid and reaction liquid was stable in composition, thefeeding flow rate of the reaction mixture was varied to adjust theresidence time. The water contents of reaction effluent, measured whenthe measured content of nitrobenzene was equal to or less than 0.1% andcalculated yield based on 4-nitrosodiphenylamine and4-nitrodiphenylamine generated was 97%, were listed below. Molar ratioof three components in complex base catalyst Tetramethyl ammoniumhydroxide: N,N-dimethyl-N,N-bis(ethoxylated (1-4 moles of ethyleneoxide) propyl) Water content No. ammonium carbonate:sodium hydroxide inproduct (%) 1 5:2:2 5.1 2 3:2:2 10.2 3 2:2:2 15.4 4 1:2:1 17.5 50.5:2:0.5 19.8 6 Tetramethyl ammonium hydroxide 1.2 is used as catalyst

It can be seen that water content at the end of the reaction increasesas the proportion of N,N-dimethyl-N,N-bis(ethoxylated(1-4 moles ofethylene oxide)propyl)ammonium carbonate in the complex catalystincreases. Namely, with the use of a complex base catalyst according tothe present invention, the range of permitted water content in thereaction mixture at the end of reaction is greatly enlarged, that is,the yield is good enough even when there is a higher content of water inthe reaction system. The less the water content is in the later phase ofthe reaction, the lower the dehydration efficiency is, thus reactiondifficulty is reduced in the process according to the present invention.If only the tetramethyl ammonium hydroxide is used as catalyst, theyield is not 97% until the water content of reaction mixture is reducedto 1.2% by dehydration, which imposes difficulty to the reaction controland increases the power consumption.

Example 19

Anhydrous complex catalyst prepared in example 12 and 651 g of anilinewere charged into a four-necked flask with stirring device andthermometer. With stirring, the temperature was elevated to 75° C. andpressure was reduced to 0.008 MPa (absolute pressure). Aniline wasreturned to the four-necked flask after demixing of the water-anilineazeotrope distilled until the water content in the system is less than0.5%. 123 g of nitrobenzene was dropwise added over 2 h, then thedehydrating was continued for 4 h. It was found via chromatographicanalysis that the yield of 4-nitrosodiphenylamine and4-nitrodiphenylamine was 97.4% and the water content in the system wasless than 0.5%.

Example 20 Comparison of Continuous Film Reaction and Complete MixingReaction

Continuous film reactions and complete mixing reactions were conductedunder the following conditions: molar ratio of aniline to nitrobenzeneto OH⁻ in complex base catalyst was controlled as 7.5:1:1, reactiontemperature was 75° C., reaction time was 5 h, and reaction pressure was0.005 MPa (absolute pressure). Results were listed in Table 2 and Table3. TABLE 2 Results of Complete Mixing Reactions Conversion rate of No.nitrobenzene % Yield % 1 98.1 94.6 2 98.3 95.1 3 98.1 94.8

TABLE 3 Results Of Continuous Film Reactions Conversion rate of No.nitrobenzene % Yield % 1 99.2 97.6 2 99.9 98.1 3 99.5 97.8

Example 21 Batch Hydrogenating Example

500 g of condensation liquid containing 17.5 weight percent of4-nitrosodiphenylamine and 3.0 weight percent of 4-nitrodiphenylaminewas charged into a 1 L autoclave with stirring device and temperaturecontrol device. 150 g of ethanol and 5 g of the powdery compositecatalyst prepared in example 1 were added thereto. The system atmospherewas replaced with hydrogen gas for three times, and then the system waspressurized to 0.8 MPa. While stirring, the reaction mixture was heatedto 100° C. and maintained at this temperature for 4 h. At the end of thereaction, the mixture was cooled, and then discharged after pressurerelease. The reaction liquid was analyzed via HPLC, and was foundcontaining no 4-nitrosodiphenylamine and 4-nitrodiphenylamine but 14.6%of 4-aminodiphylamine (chromatograph content).

Comparison of Powdery Composite Catalyst and Noble Metal Catalyst

Pd/C catalyst with 5 wt. % of palladium was compared with the powderycomposite catalyst according to the present invention. Experiments werecarried out under the same conditions as described in above batchhydrogenating example. The quantity of catalysts used was the same, andboth Pd/C catalyst and powdery composite catalyst were recovered andreused after the reaction. Within 21 times of reuse,4-nitrosodiphenylamine was undetectable in both reaction liquids.However, at the twenty-first time of reuse, the reaction liquid obtainedby using Pd/C catalyst was found containing 0.1 wt. % of4-nitrodiphylamine while the reaction liquid obtained by using thepowdery composite catalyst according to the present invention was foundcontaining no 4-nitrodiphylamine. The results showed that the antitoxicperformance of the powdery composite catalyst according to the presentinvention was better than that of the noble metal catalyst.

1. A process for preparing 4-aminodiphenylamine comprising reactingnitrobenzene and aniline in presence of a complex base catalyst to forma reaction mixture; hydrogenating the reaction mixture in presence ofhydrogen, a powdery composite catalyst, and a hydrogenation solvent;separating, recovering, and reusing the complex base catalyst and thepowdery composite catalyst from the reaction mixture; separating,recovering, and reusing aniline, and optionally water, from the reactionmixture; refining the reaction mixture to obtain 4-aminodiphenylamine,wherein the complex base catalyst comprises tetraalkyl ammoniumhydroxide, and tetraalkyl ammonium salt.
 2. The process of claim 1,where the complex base catalyst further comprises alkali metalhydroxide.
 3. The process of claim 1, wherein the powdery compositecatalyst comprises nickel, aluminum, and a component A that is at leastone selected from the group consisting of Fe, Cu, Co, Mn, Cr, Mo, B andP.
 4. The process according to claim 1, wherein the condensationreaction is carried out under conditions of a molar ratio ofnitrobenzene to aniline of from 1:1 to 1:15, a reaction temperature offrom 20 to 150° C., a reaction pressure of from 0.005 to 0.1 MPa(absolute pressure), and a reaction time of from 3.5 to 6 hours.
 5. Theprocess according to claim 1, wherein a molar ratio of hydroxide ion inthe complex base catalyst to nitrobenzene is in a range of from 1:4 to4:1.
 6. The process according to claim 1, wherein the reaction ofaniline and nitrobenzene is carried out in the absence of oxygen.
 7. Theprocess according to claim 1, wherein proton material is not controlledduring the reaction of aniline and nitrobenzene.
 8. The processaccording to claim 1, wherein the hydrogenation reaction is carried outat a volume ratio of hydrogen gas to a sum of the hydrogenation solventand the reaction mixture in a range of from 10:1 to 1500:1, a weightratio of the powdery composite catalyst to the sum of the hydrogenationsolvent and the reaction mixture in a range of from 0.5:100 to 16:100,and a weight ratio of the hydrogenation solvent to the reaction mixturein a range of from 1:10 to 5:10.
 9. The process according to claim 8,wherein a reaction temperature of the hydrogenation reaction ranges from50 to 100° C., a reaction pressure of the hydrogenation reaction rangesfrom 0.2 to 3.0 MPa (absolute pressure), and the reaction time rangesfrom 2 to 7 hours.